Is This A Virus?!?

Yup. It's called MacDefender.

you can remove it by following these instructions.

 

Does the first section of this apply?

Mac Virus/Malware Info by GGJstudios
There are currently no viruses for Mac OS X in public circulation, only a handful of trojans and other malware, which have to be installed manually via entering the administrator password.
The only anti-virus you need to protect your Mac is education and common sense.​

 

Here is a better set of instructions on how to remove MACDefender/MacSecurity/MacProtector.

 

It's not a virus. Did you actually install the downloaded app? If you did, you installed a trojan. Never click to allow anything that offers to clean up or remove malware from your computer, unless you know what the app is and you intentionally installed it and allowed it to run.

I know it's been posted already, but it bears repeating: Read this: Mac Virus/Malware Info, especially the first section on MacDefender. If you did install it, you can follow the other removal instructions or do it manually. The only effective method for complete app removal is manual deletion:

Best way to FULLY DELETE a program​